A capacitance information recording and playback system has been disclosed by Clemens in U.S. Pat. Nos. 3,842,194, 3,842,217 and 3,909,517. In this system, a plastic disc record is prepared having geometric variations in a spiral groove in a disc surface which variations represent audio and video information. The disc record is coated with a conductive layer and a dielectric layer. A stylus having a conductive electrode is used to reconstitute the information as an electrical signal.
Other systems have been devised based on a capacitance readout in which the disc record does not require a grooved surface. In either the grooved or the non-grooved system a further improvement has been made whereby conductive plastic molding composition may be employed to form the disc record, thereby eliminating the need for separate conductive and dielectric layers.
Generally, the conductive disc records are prepared from a plastic molding composition containing conductive particles (e.g., carbon black), a molding resin such as a vinyl chloride homopolymer or copolymer and various additives such as lubricants, stabilizers, flow modifiers, and the like.
In a manufacturing environment where thousands of disc records are produced daily, a fast and reliable quality control method is required to analyze the carbon black content of the plastic molding composition as well as the disc records molded therefrom.